1. Technical Field
The present disclosure relates to epitaxial structures and methods for making the same.
2. Description of Related Art
Light emitting devices such as light emitting diodes (LEDs) based on group III-V nitride semiconductors such as gallium nitride (GaN) have been in use in many applications.
Since wide GaN substrates cannot be produced, the LEDs have been produced on a heteroepitaxial substrate such as sapphire. The use of sapphire substrate is problematic due to lattice mismatch and thermal expansion mismatch between GaN and the sapphire substrate. One consequence of thermal expansion mismatch is straining of the GaN/sapphire substrate structure, which leads to cracking of the GaN/sapphire substrate and difficulty in fabricating devices with small feature sizes. A solution to cure the thermal expansion mismatch is to form a plurality of grooves on the surface of the sapphire substrate by lithography or by etching before growing the GaN layer. However, both the processes of lithography and etching are complex, high in cost, and may contaminate the sapphire substrate.
What is needed, therefore, is to provide a method for solving the problem discussed above.